Torque Motor Types and Applications
Torque motors are motors with a particularly high torque. This means that an additional gearbox can often be dispensed with. This is why torque motors are also referred to as direct drives. These electric motors are usually relatively short compared to high speed motors. On the other hand, high torque motors usually have a large diameter. The large diameter of the rotor ensures a high torque in the lower speed range. High speed motors, on the other hand, usually have a small diameter. And are usually relatively long. The torque of high speed motors is much smaller in comparison, but they achieve higher speeds. In most cases, the torque drops much faster with high torque motors. However, this depends heavily on the type of electric motor that is used as a high torque motor. In the YouTube video below, all the main high torque motor types are presented.
Types of High Torque Motor
AC motors and BLDC motors without brushes are primarily used for torque motors. These are often also referred to as brushless DC motors. There are two motor designs of high torque electric motors that are primarily used. These are axial flux motors and radial flux motors. Radial flux motors can be further subdivided into two different types. These are motors with internal rotors and external rotors. External rotors are primarily used for high torque radial flux motors. Transverse flux motors can also generate high torques. However, they are very rarely used in industry. Permanent magnets are generally used for all these types of electric motor. This is because permanent magnets can get a higher torque out of the motor with the same phase current. However, it is of course also possible to build a high torque motor without permanent magnets. For example, as a reluctance motor with an external rotor. In the YouTube video below you can watch an animation of a high torque reluctance motor.
Video about High Torque Motors
Design of High Torque Motors
So what makes a high torque motor so special? The secret of high torque motors is primarily the large diameter. This is the main reason why axial flux motors and external rotor motors are often used. Because these types of electric motors are well suited for short motors with a large diameter. It is not the outer diameter of the rotor that is important, but the diameter of the central air gap. This is where the mechanical forces between the rotor and stator are generated by the magnetic flux. The larger the diameter where these forces arise, the greater the resulting torque. Of course, it is also possible to build high torque motors with a small diameter, but this is not so easy. Another important characteristic of high torque motors is the high number of permanent magnets. However, the combination of stator and rotor poles should always be a good match. Another important point is the strength and thickness of the permanent magnets. The stronger and thicker the permanent magnets are made, the bigger the torque will be. Of course, the torque can only ever be increased within certain limits. And the maximum speed that the electric motor can achieve also decreases as a result. This is because the back EMF also increases when stronger magnets are used. There are of course other ways to increase the torque. For example, by using a smaller air gap or a higher phase current from the inverter.
Advantages and Disadvantages of High Torque Motors
Due to the high torques of high torque electric motors, an additional gearbox is no longer necessary in many cases. This eliminates the losses of a gearbox and increases the overall efficiency of the electric drive. This is because it only consists of the high torque motor and the inverter or power electronics. This is a great advantage for electric boats and electric airplanes, for example. But it is also good for electric motorcycles and mobile robots. However, high torque motors without a gearbox are usually larger than electric motors with a gearbox. This is because the high torque motor usually has a lower speed than a motor with a gearbox. Due to the lower speed, high torque motors also usually have a lower power density. However, the overall size of high torque motors is usually comparable with drives that have a gearbox. However, this is of course also heavily dependent on the type of gearbox that is used.
Applications of High Torque Motors
There are two main applications for which high torque motors are particularly good. The first is applications where high dynamics and high accuracy are required. In other words, applications where an object needs to be moved quickly and very precisely from point A to point B. These include, for example, industrial robots, machine tools and production machines. On the other hand, high torque motors are especially useful for applications where high efficiency is required. For example, for long ranges of electric motorcycles and airplanes.
Mobile Applications with Torque Motors
Because of the high torques of high torque electric motors, an additional gearbox is in many cases no longer necessary. This eliminates the losses of a gearbox and increases the overall efficiency of the electric drive. The higher overall efficiency is also noticeable when braking. This means that more energy can be recovered during braking than with a drive system with a gearbox.
Industrial applications with torque motors
Thanks to their excellent dynamics, high torque motors are also used in production machines, robots and machine tools. In order to accelerate the masses of machines with high torques more quickly. By eliminating the need for a gearbox in a machine tool, a high torque motor not only allows workpieces to be machined faster, but also more precisely. In production machines, maintenance costs can be reduced by eliminating gearboxes and using high torque motors. This is because it only consists of the high torque motor and the inverter or power electronics.